Good grief...
You don't make your sources available to the public if you don't intend for people to modify and share. If you release your source to public don't boo hoo when Bob does something with it you don't like. Any normal, rational human being that writes software knows that you can't control what people do with the source and the author would be wasting his time trying to enforce a wierd-o license against people doing what they naturally do with source thats freely available, which is tweak and share.
Most of the points brought up by various people in here are certainly valid, but they mostly apply to commercial settings, and with commercial products. The contractual and licensing issues that have been put forth for discussion certainly do make sense in commercial settings. In these instances, the code does come with specific and very detailed circumstances that absolutely should be followed, but lets face it, this is in relation to source that isn't public released and thus it doesn't really relate to this thread now does it?